Multnomah County has piled onto a lawsuit against a North Carolina bridge materials company, adding heft to allegations new decking on the Morrison Bridge is faulty and should've never been installed.

Earlier this month, a Multnomah County Circuit Court judge formally approved a motion by the county to toss in its lot with Conway Construction, the Washington-based contractor that installed the new bridge deck in 2011 and 2012. In a suit filed last year—and revised earlier this year to include fresh claims—Conway says the fiber-reinforced polymer (FRP) materials supplied by Durham-based ZellComp Inc. are "defective" and were "not appropriate nor adequate" for the $4.2 million project.

Conway's suit says screws in the deck are coming undone, that polymer panels are shifting under the weight of passing vehicles, and that the problem's getting worse. The suit asks for a full refund of the more-than $1.3 million paid for the decking material.

ZellComp President and CEO Dan Richards has acknowledged "minor" issues, but says there's no reason to believe his product is at fault.

The county has so far declined to comment on the issue—other than to reiterate that the bridge is still safe—but Conway purports to get much of its information about the Morrison's problems straight from county engineers. The decision to join up with the litigation rather than file a separate suit suggests Multnomah County officials largely concur with Conway. But Stephen Kelly, the private attorney representing the county in the matter, has yet to file accusations, so it's unclear exactly what remedy officials are seeking.

The deck project—a bid to replace the bridge's slippery, cracked steel grating with something safer—began in 2011 and was plagued with problems from the outset. County officials nearly shut the effort down that summer over concerns Conway was letting toxic material fall into the Willamette River. In the end, though, the county reached an understanding with the company. The Morrison—Portland's busiest non-highway bridge—reopened in March of last year.

It's not the first county bridge to have problems with FRP decking—a relatively new material still considered experimental . As the Mercury's reported, new decking installed on the Broadway Bridge in 2005 began cracking and coming apart shortly thereafter. The hollow panels also started filling with rainwater, adding significant weight to the drawbridge spans.

That decking was supplied by a ZellComp competitor, Martin Marietta Materials, and officials remedied the problems partly by replacing out the faulty panels with ZellComp product. Yet when they were looking to source supplies for the Morrison Bridge deck replacement, county staffers initially tried to skirt a public bidding process and purchase only from Martin Marietta, according to documents obtained by the Mercury.

ZellComp protested, eventually submitted the winning bid, and here we are.